Abstract
A low fertilizer application technique was studied for summer welsh onion by applying a release-controlled fertilizer to substrate in chain pots. 1. The nitrogen release rate of a coated ammonium nitrate phosphate (2401-100S) of a 100-day sigmoid type for suppressed initial nitrogen release was 3.3% during the period of raising seedlings. No high-concentration damage was observed on welsh onion nursery plants, which grew as well as standard cultivation nursery plants. 2. Under a constant amount of top dressed nitrogen (standard application rate of nitrogen, 160kg ha^<-1>), the amount of nitrogen from 60kg ha^<-1> of the 100-day type coated ammonium nitrate phosphate by the application method in the chain pot system yielded an equivalent harvest to that from a standard application rate (basal dressing nitrogen, 80kg ha^<-1>). From the nitrogen release rate of this fertilizer, top dressing applied three times was judged adequate in contrast to four applications prescribed for the standard application rate. 3. When 60kg ha^<-1> of the 100-day type coated ammonium nitrate phosphate was applied in the chain pots, 90kg ha^<-1> of top dressed nitrogen resulted in an equivalent harvest to that from the standard application rate. The total amount of applied nitrogen was 150kg ha^<-1>, which was 38% lower than 240kg ha^<-1> from the standard application rate of nitrogen. The utilization ratio of applied nitrogen also increased to 43% in contrast to 25% for the standard application rate. 4. Soil nitrate in the soil after cultivation from the application method in the chain pot system was lower in all soil horizons ranging 0-60cm than that from the standard application rate.
